Get The Underground 2 running

I'll try and fix as much as possible to get #3737 (closed) resolved, but the mod desperately needs a better patch than the one provided in that issue. It also needs a good seizure warning.

The story so far:

• SetHello is getting called from an activator, which crashes the script.
• Another activator StartScripts the script attached to your companion, which then crashes because the reference isn't an NPC, and takes down the script that's still attached to the NPC in question along with it.
• Asking your companion to strip doesn't work due to equip's implicitly added items triggering an equip.

Unresolved things that could maybe get their own issues:

• An NPC running into (up against) a forcefield doesn't trigger GetCollidingActor from said forcefield. This appears to be vanilla behaviour as well.
• Gravity shouldn't apply to actors with nothing beneath them. This breaks a haunted house. #5862
• Followers don't follow you through intervention/recall. #5863 (closed)

Issues I'm going to ignore:

• A guy in a cage absolutely tanking my frame rate.
• A dead NPC (CS health: 0) that gets PositionCelled into the room can apparently AiActivate a lever (assuming the script isn't also broken in vanilla). I can't get that to happen if I use the console to SetHealth 0 and AiActivate stuff though.